1. Field of the Invention
The present invention relates to a scroll compressor which is installed in an air conditioner, a refrigerator, or the like.
2. Description of Related Art
In conventional scroll compressors, a fixed scroll and an orbiting scroll are provided by engaging their spiral wall bodies, and fluid inside a compression chamber, formed between the wall bodies, is compressed by gradually reducing the capacity of the compression chamber as the orbiting scroll revolves around the fixed scroll.
The compression ratio in the design of the scroll compressor is the ratio of the maximum capacity of the compression chamber (the capacity at the point when the compression chamber is formed by the meshing of the wall bodies) to the minimum capacity of the compression chamber (the capacity immediately before the wall bodies become unmeshed and the compression chamber disappears), and is expressed by the following equation (I).
Vi={A(xcex8suc)xc2x7L}/{A(xcex8top)xc2x7L}=A(xcex8suc)/A(xcex8top)xe2x80x83xe2x80x83(I)
In equation (I), A(xcex8) is a function expressing the cross-sectional area parallel to the rotation face of the compression chamber which alters the capacity in accordance with the rotating angle xcex8 of the orbiting scroll; xcex8suc is the rotating angle of the orbiting scroll when the compression chamber reaches its maximum capacity, xcex8top is the rotating angle of the orbiting scroll when the compression chamber reaches its minimum capacity, and L is the lap (overlap) length of the wall bodies.
Conventionally, in order to increase the compression ratio Vi of the scroll compressor, the number of windings of the wall bodies of the both scrolls is increased to increase the cross-sectional area A(xcex8) of the compression chamber at maximum capacity. However, in the conventional method of increasing the number of windings of the wall bodies, the external shape of the scrolls is enlarged, increasing the size of the compressor; for this reason, it is difficult to use this method in an air conditioner for vehicles and the like which have strict size limitations.
In an attempt to solve the above problems, Japanese Examined Patent Application, Second Publication, No. Sho 60-17956 (Japanese Unexamined Patent Application, First Publication, No. Sho 58-30494) proposes the following techniques.
FIG. 9A shows a fixed scroll 50 of the above application comprising an end plate 50a and a spiral wall body 50b provided on a side surface of the end plate 50a. FIG. 9B shows an orbiting scroll 51 similarly comprising an end plate 51a and a spiral wall body 51b provided on a side surface of the end plate 51a. 
A step portion 52 is provided on the side surface of the end plate 50a of the fixed scroll 50. The step portion 52 has two parts in which one part is high at the center of the side surface of the end plate 50a and the other part is low at the outer end of the end plate 50a. Furthermore, corresponding to the step portion 52 of the end plate 50a, a step portion 53 is provided on a spiral top edge of the wall body 50b of the fixed scroll 50. The step portion 53 has two parts in which one part is high at the center of the spiral top edge and the other part is low at the outer end of the spiral top edge. Similarly, a step portion 52 is provided on the side surface of the end plate 51a of the orbiting scroll 51. The step portion 52 has two parts in which one part is high at the center of the side surface of the end plate 51a and the other part is low at the outer end of the end plate 51a. Furthermore, corresponding to the end plate 51a of the step portion 52, a step portion 53 is provided on a spiral top edge of the wall body 51b of the orbiting scroll 51. The step portion 53 has two parts in which one part is high at the center of the spiral top edge and the other part is low at the outer end of the spiral top edge.
FIG. 10A is a plan view of the orbiting scroll and FIG. 10B is a cross-sectional view taken along line Ixe2x80x94I of FIG. 10A. The perpendicular length (lap length) of the wall body which is further out than the step portion 52 is represented by H. The step difference of the step portion 52 is represented by L. The perpendicular length (lap length) of the wall body which is further in than the step portion 52 is represented by H2.
As shown in FIG. 10B, the lap length H of the wall body which is further out than the step portion 52 is longer than the lap length H2 of the wall body which is further in than the step portion 52. The maximum capacity of the compression chamber P increases as the lap length of the wall body which is further out than the step portion 52 becomes larger, in comparison with the maximum capacity of the compression chamber having the uniform lap length. Consequently, the compression ratio Vi in the design can be increased without increasing the number of spiral laps of the wall body. Furthermore, since the lap length of each step is short, concentration of stress can be avoided.
However, when the compression ratio Vi is increased as described above, the following problems are generated. As shown in FIG. 11, as the compression ratio Vi is increased, the pressure rapidly increases according to the rotating angle. Furthermore, a gap tends to remain at the engaging parts between the step portions 52 and 53 due to machining tolerance or the like. If the length L is great, the amount of leakage of refrigerant from the compression chamber is increased.
In other words, when L/H is increased in order to increase the compression ratio Vi, theoretical efficiency is increased; however, in fact, the amount of leakage of refrigerant via the engaging part between the step portions 52 and 53 from the compression chamber is increased because of high pressure and increase of the height L. Therefore, there is a problem that the compression efficiency of the scroll compressor decreases due to leakage.
In view of the above problems, an object of the present invention is to provide a scroll compressor in which the compression efficiency is increased.
An aspect according to the present invention is to provide a scroll compressor comprising a fixed scroll which is fixed in position and has a spiral wall body provided on one side surface of an end plate; an orbiting scroll which has a spiral wall body provided on one side surface of an end plate, being supported by engaging of the wall bodies so as to orbit and revolve around the fixed scroll without rotation; a first step portion provided on the end plate of one of the fixed scroll and the orbiting scroll, being at a high level at a center side and at a low level at an outer end side along the spiral wall body on one side surface of the end plate; and a second step portion provided on a top edge of the wall body of the other of the fixed scroll and the orbiting scroll by dividing the top edge into plural parts, the second step portion being at a high level to at a low level from the outer end to the center in correspondence with the first step portion, wherein, when a length of the wall body is represented by H at the outer side from the first step portion and a step difference of the first step portion is represented by L in the one scroll, L/H is 0.2 or less.
As described above, since the amount of leakage is increased as L/H is increased, a compression efficiency decreases. FIG. 12 is a graph showing a relationship between L/H and compression efficiency. As shown in FIG. 12, if L/H is 0.2 or less, a superior scroll compressor is obtained by preventing decrease of the compression efficiency and avoiding concentration of stress. Furthermore, the scroll compressor has satisfactory compression efficiency by avoiding leakage of refrigerant.